Communication networks include a collection of resources that are employed to transport user information from origination nodes to destination nodes. The resources include switching nodes and communication links. In a packet switching network, user information takes the form of packetized digital data. The user information is carried in discrete individual packets, and each individual packet carries its own destination address along with at least a portion of the user information. Switching nodes evaluate the destination addresses to determine how to appropriately route the packets.
Service providers which operate communication networks and network users benefit from improved network efficiency. Service providers want improved efficiency because they can generate greater revenue by transporting a greater amount of user information using a given collection of network resources. Users want improved efficiency because the costs of providing the network resources can then be spread over a greater number of user information transfers to lower the costs of transporting any single item of user information.
In communication networks, and particularly satellite communication systems, any single network node, such as a satellite, is often required to process only a fraction of the total channels available to the network. A channel is typically processed by receiving a wideband signal, decomposing the wideband signal into many narrowband signals, demodulating the narrowband signal which conveys a channel of interest, picking the channel of interest out of a specific time slot if TDMA communication schemes are employed, and performing any repackaging, modulation, combination, or other function needed to pass the information obtained from the channel of interest toward its ultimate destination.
Different nodes process different channels from the total network allocation. All channels are used, but the usage is spread over many different nodes. From time to time, the mix of channels processed at the nodes changes. When nodes reside in satellites orbiting the earth in moving orbits, the mix of channels processed at the nodes can change on a minute by minute basis. Accordingly, network nodes are typically configured to process a greater number of channels than they actually need to process at any given instant. This type of configuration leads to inefficiencies which have particularly serious consequences when the nodes are located in earth-orbiting satellites.
In a code division multiple access (CDMA) system, a number of users are superimposed over each other in the same frequency channel. These codes operate with multiple code symbols per user bit on each user and spread the energy for each user over a broader spectrum than would otherwise be required. The codes can be superimposed over each other as long as they are mutually orthogonal.
Unfortunately, conventional packet switching and other networks are operated in a relatively inefficient manner. Inefficiencies result when header information must be attached to data packets so that routing can be performed. This can lead to the consumption of system resources such as communication links to transport routing information instead of user information. The portion of link bandwidth which is used to transport header information cannot be used to transport user information, and this results in an inefficient use of network resources.
While the problems associated with the inefficient use of network resources plague a wide variety of communication networks, they have more serious consequences in networks which rely on RF communication links.
There is also a significant need for apparatus and methods for providing more efficient routing of user information within a satellite communication system. In addition, there is a significant need for apparatus and methods for increasing the utilization of the on-board resources of orbiting satellites by small modifications to the satellites and terrestrial equipment.